The U.S. Pat. No. 3,062,416 to Cooprider, issued Nov. 6, 1962, discloses a liquid dispenser comprising a hollow body and a one-piece plunger including an actuator/piston. The piston has an enlarged head at its lower end inside the hollow body. Inlet and outlet check valves are provided and a spring urges the plunger upward.
In assembly, after the Cooprider plunger is installed in the body, a tool is brought down against the upper end of the body. The lower end of the tool is so shaped as to cause the plastic of the body to be swaged inwardly thus providing a blocking flange to trap the plunger in the body.